Electronic meters of the flat-bed printer type are well-known and are described for example in U.S. Pat. No. 4,579,054, issued to Buan, et al, which shows a stand-alone electronic mailing machine in which the electronic postage meter forms an integral part of the device. Other aspects of such a stand-alone mailing machine are described in U.S. Pat. Nos. 4,535,407 and 4,523,523 among others.
Of particular concern in postage meters and mailing machines is the prevention of unauthorized printing of a meter impression. That is, since the printing of the impression assumes that the Post Office has been paid for the delivery of the mail piece, the making or "wiping" of a print without accounting for the value will result in loss of revenue to the Post Office to cover the costs of delivery. It will be appreciated that in an area of such concern, many devices have been developed to solve problems associated with the security of the printing die.
Die protection assemblies incorporate various mechanical arms or projections which protrude from the printwheel area of the die in order to prevent a person from simply placing an envelope against the die to obtain an imprint.
U.S. Pat. No. 2,795,186 issued to Bach shows a movable shroud which can be lowered to guard the printing die agains taking unauthorized impressions at any time between printing operations. The shroud completely covers the face of the value printing die when the printing mechanism is not in an operating cycle and is locked in that position until the cycle starts at which time the shroud moves to a position uncovering the die. U.S. Pat. No. 4,559,444 issued to Erwin et al. teaches an interposer arrangement which extends upward from the platen into the space into which an envelope or other workpiece is to be inserted. These interposers are moved out of the way during a legitimate printing operation. The interposer blades are mechanically linked to the inking mechanism in order to move the blades out of the way as the mailpiece moves into position for imprinting. U.S. Pat. No. 4,796,526 entitled Value Printing Die Protection Device in an Electronic Postage Meter Machine and U.S. Pat. No. 4,796,527 entitled Value Printing Die Protection Mechanism in a Postage Meter Machine describe interposer devices which are linked to the motor driving the platen of the printer to move out of the way or actuated by a power switch to be moved out of the way so long as power is applied to the machine.
While these known devices work well in the particular environments in which the platen and the die are not expected to be physically separated, in a modular device where the meter with its secure die is removable from the assembly where the platen is retained, several new security issues are created in respect of a flat-bed printer type of postage meter.